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Parallel Rules

Parallel rules help draftsmen, surveyors, cartographers, architects, and navigators draw accurate parallel lines. The instrument comes in two main forms: two rectangular straight edges connected by brass or silver hinges, or a single frame surrounding a roller. The first type was known in Europe by 1600, while Englishman A. George Eckhardt is credited with inventing the second in 1771. The parallel rule was superseded for most uses by the T-square in the 19th century, but navigators continue to use parallel rules in conjunction with gridded charts.

The mathematics collections contain about twenty parallel rules and combination instruments, dating from the late 18th century to the late 20th century and ranging in length from 6 to 24 inches. The objects are made from ebony and other woods, brass, German silver, and plastic. They were manufactured in the United States, England, Italy, and Taiwan. They were used for military surveying, in navigation, in business, in art and technical drawing, and for placing handles on caskets. Several of the objects in this group illustrate innovations added to the basic instrument.

Acknowledgement

The digitization of this group of artifacts was made possible through the generous support of Edward and Diane Straker.

This brass semicircular protractor is divided by single degrees and marked by tens from 10° to 90° to 10°. It is attached with metal screws to a set of brass parallel rules. Brass S-shaped hinges connect the rules to each other. The bottom left screw on the parallel rules does not attach to the bottom piece. A rectangular brass arm is screwed to the center of the protractor. A thin brass piece screwed to the arm is marked with a small arrow for pointing to the angle markings. The protractor is stored in a wooden case, which also contains a pair of metal dividers (5-1/4" long).

The base of the protractor is signed: L. Dod, Newark. Lebbeus Dod (1739–1816) manufactured mathematical instruments in New Jersey and is credited with inventing the parallel rule protractor. He served as a captain of artillery during the Revolutionary War and made muskets. His three sons, Stephen (1770–1855), Abner (1772–1847), and Daniel (1778–1823), were also noted instrument and clock makers. The family was most associated with Mendham, N.J. (where a historic marker on N.J. Route 24 indicates Dod's house), but Dod is known to have also lived at various times in Newark.

ID number MA*310890 is a similar protractor and parallel rule. Compare also to a Dod instrument owned by the Metropolitan Museum of Art in New York, http://www.metmuseum.org/Collections/search-the-collections/5535.

This brass parallel rule has a semicircular protractor attached to the top blade. The protractor is divided to degrees and marked by tens from 10 to 90 to 10. A movable arm attached to the origin point of the protractor contains a vernier, which was intended to permit the measurement of angles to 5 minutes of accuracy. The hinges connecting the blades of the rule are straight. There is no maker’s mark.

Mathematician James McKenna gave this measuring instrument to the Smithsonian. He reported that an ancestor used it at Bedford, Pa., before 1800. A name, scratched on one of the tools in the set of drawing instruments (MA*310891) that accompanied this protractor, suggests that the ancestor was John A. Stuart, who surveyed a line in Bedford County on Wills Mountain that continues to bear his name.

A 14" trapezoidal mahogany frame with metal end pieces covers two mahogany rollers that rotate on metal shafts. A paper label is marked: CARRINGTON'S PATENT PARALLEL RULER, FOR COUNTING HOUSES, &C. The label is decorated with an eagle over a shield with arrows in its claws. The eagle's beak holds a banner marked: E PLURIBUS UNUM.

On April 14, 1832, James Carrington of Wallingford, Conn., patented a parallel ruler that was later manufactured by William Hill of Wallingford. The rollers were raised in order to prevent ink from smearing as the ruler was moved across a drawing. In 1849 the U.S. House of Representatives ordered six dozen of the rulers from R. Farnham, a stationer in Washington, D.C., for $2.30 per dozen. This suggests the rules were used relatively widely for a significant period of time. Before he built a dam and factory in Wallingford around 1830, Carrington was a supervisor and inspector at the Harpers Ferry and Springfield armories.

This instrument has a wooden handle attached by a large brass thumbscrew to a brass protractor that is divided to single degrees and numbered by tens in both directions from 10 to 170. The protractor is screwed to a rectangular brass piece that slides in a groove in a rectangular wooden guide-piece. The guide-piece has brass clamps and thumbscrews for affixing the instrument on a table. The protractor is also attached by a split nut to a metal screw shaft that runs the width of the instrument. A thumb rest and gear on the left clamp rotates the screw shaft.

A T-square is a technical drawing instrument used by draftsmen primarily as a guide for drawing horizontal lines on a drafting table. In this instrument, the two blades of the T-square are not fixed in a perpendicular position but rather can be rotated to any angle on the protractor. The large thumbscrew can then be used as a handle to move the blades along the screw shaft, allowing the user to draw parallel lines.

Eugene James Towne (1847–after 1900) of North Dana, Mass., received a patent for this device in 1877. He submitted this example with his application as a prototype for the instrument, and the U.S. Patent Office marked it on the bottom: 187330 (/) L.1201.1228. Towne, a cabinetmaker, and J. W. Goodman, who made pianos, billiard table legs, and other wooden items in North Dana, apparently intended to manufacture the device together. However, the instrument likely was not widely adopted.

One rule is 24" long and is held together by corroded brass hinges. The blades may be solid ebony. Small metal buttons in the center of each blade assist with positioning the instrument. This rule has no identifying markings.

The second rule is 18" long and is held together by nickel plated brass hinges. The blades are made of ebonized boxwood. Two metal knobs at the center of each blade are used to position the instrument. On the left of the knob on the top blade is marked: KEUFFEL & ESSER CO (/) N.Y. Below the knob is marked: 1784. On the right of the knob is marked: TRADEMARK (below the K&E lion logo). The bottom blade is marked: PAT. JUNE 1, 1915.

By 1880 Keuffel & Esser of New York imported ebony parallel rules with brass hinges and positioning buttons, selling the 24" size as model 706 for $2.00. By 1890 the firm was also making its own version of the rules, since the imported wood, which was often grown in Africa, warped and shrank in the climate of the United States. The imported rules were sold as model numbers 1790 (6", 35¢) through 1795 (24", $1.75). K&E stopped selling imported ebony rules in 1909. Rules manufactured at the company's factory in Hoboken, N.J., from hardwoods stained black were sold as model numbers 1780 through 1785. The 18" model 1784 was priced at $1.25 in 1890 and $1.50 in 1913. The company discontinued this product line after 1936, when model 1784 sold for $2.50.

The first rule thus dates to between 1880 and 1909. Charles Christ Pfeiffer (b. 1874) received the patent mentioned on the second rule, for replacing one of the rivets securing one of the hinges with an adjustable screw. He emigrated from Germany as a child and worked as a cabinetmaker and foreman in Hoboken, possibly for K&E since he assigned the patent to the company. In the 1920s Pfeiffer moved to New London, Conn., where he purchased a farm in the 1930s. The second rule dates to between 1915 and 1936.

This 24" boxwood instrument has two blades held together by three metal (possibly copper) hinges. The middle hinge is curved and has a slide with a thumbscrew that allows the user to fix the separation between the blades at a desired width. This hinge is marked: PAT APL'D FOR. The top blade is 1/2" wide and 22" long. The bottom blade is 7/8" wide, divided to 1/2", and numbered by ones from 1 to 12 to 1. The back is marked: D. W. BELLOWS (/) MFR. (/) PAWTUCKET, R.I.

Dexter W. Bellows (1856–1940) was a funeral director in Pawtucket, R.I., from 1892 until his death. He designed this rule in 1896 to assist in placing handles evenly along the sides of caskets. No patent record has been found, but the National Casket Company of Baltimore is known to have distributed the rule.

This 18" brass instrument has rollers mounted 2-5/8" from each end and connected by a shaft with a brass cover. Both ends have knobs to hold while rolling the parallel rule over a drawing. The center top of the base is marked: KEUFFEL & ESSER Co (/) NEW YORK. The center bottom is marked: 1758. A plain wooden box has a sliding lid that is marked: Parallel (/) Rule 3. It is also marked: 18". It is also marked (facing the other direction): R. The side of the box is marked: Rolling Parallel Rule K & E – 1758 – 18".

Keuffel & Esser began to sell model number 1758 between 1881 and 1890, but there was no brass cover over the shaft and the instrument weighed only 40 oz. Between 1899 and 1906, K&E introduced the cover. The rule then weighed 54 oz. and sold for $12.00. In 1927, the company began to offer the instrument in a case covered with synthetic leather instead of in a plain wooden box.

The lower blade of this 24" brass hinged parallel rule is marked: KELVIN – WHITE CO. BOSTON – NEW YORK. The instrument has one rectangular wooden handle and one rectangular black plastic handle. Both handles are attached by crude welding. They may have been added by the previous owner, since Kelvin & White catalog advertisements show round knobs in 1931 and no handles in 1940. The side and top edges of the rule are divided as a rectangular protractor, numbered by tens from 180 to 10 and from 360 to 180. Unlike MA*309661, MA*309662, and MA*309663, the bottom edge is not divided for a protractor or nautical compass points.

Australian shipbuilder Wilfrid O. White (1878–1955) studied in Glasgow, Scotland, with William Thomson, Lord Kelvin (1824–1907), before settling in Boston in 1902. White served as an agent for the Glasgow instrument workshop in which Kelvin held an interest until 1919, when White established the American firm of Kelvin & Wilfrid O. White. The company was renamed Wilfrid O. White & Sons, Inc., in 1950. Throughout its existence the firm charged $28.00 for the 24" brass version of "Captain Field's improved parallel rule," model number 554. The markings in this example are like those shown in the 1940 catalog.

This clear plastic ruler has two aluminum hinges and small positioning knobs that may be tightened or loosened. The lower left and upper right corners of the blades are marked: 18". The hinges are marked: THE C-THRU RULER CO. (/) BLOOMFIELD, CONN. U.S.A. Six circular slices of cork on the bottom of the instrument protect the surface on which it is used.

Teacher Jennie Zachs established the C-Thru Ruler Company of Hartford, Conn., in 1939. Although the firm was acquired by Acme United Corporation in 2012, it continues to make drafting tools and drawing instruments, including an aluminum version of this instrument. For other C-Thru products, see 1984.1071.12 and 1988.0807.02.